1. Field of the Invention
The present invention relates to a digital echo circuit which generates an echo of a musical sound signal by using a digital signal processing technique, so as to reproduce an analog echo sound.
The present application is based on Japanese Patent Application No. Hei. 10-286083, which is incorporated herein by reference.
2. Description of the Related Art
A recent karaoke apparatus has a function of adding various effects and an echo to vocal sound by using a digital signal processing technique. FIG. 2 shows a related digital echo circuit which adds an echo to a musical sound signal such as vocal sound. An input musical sound signal is converted into a digital signal by an A/D converter 10. An amplifier 12 adds an input gain to the digital signal. The resulting digital signal is supplied via an adder 14 to a digital delay circuit 16 so as to be delayed by a predetermined time thereby. The characteristics of the output data of the digital delay circuit 16 are appropriately corrected by an equalizer 18. A feedback gain is added to the corrected output data by an amplifier 20. The corrected output data is then fed back to the adder 14 to be added to input data. The echo signal data which is produced in the feed back loop 22 is returned to an analog signal by a D/A converter 24. In a mixing circuit 26, the analog signal is mixed with the original musical sound signal (dry sound signal) and then output. The reverberation time of the echo is adjusted by the input gain which is added by the amplifier 12, and the feedback gain which is added by the amplifier 20.
In the digital echo circuit of FIG. 2, an echo is generated by using a digital signal processing technique. Therefore, the generated echo is free from distortion and fluctuation, and results in an excessively regular echo. As compared with an analog echo, the digitally generated echo produces a simple effect and is heard as a cold sound.
It is an object of the present invention to provide a digital echo circuit which can solve the problem of the related art, and can reproduce a sound of an analog echo.
In the present invention, in a digital echo circuit in which a musical sound signal data configured by a digital signal is supplied to a feedback loop having a digital delay circuit thereby generating an echo. A digital signal processing circuit is disposed in the feed back loop, and adds data corresponding to distortion components of an analog signal to the musical sound signal data in the feedback loop. According to the present invention, waveform distortion components are added to the generated echo signal, so that distortion components and the like due to recording and reproducing processes of a tape-recorder-type analog echo can be reproduced, and a warm echo similar to an analog echo can be obtained.
For example, the digital signal processing circuit which adds data corresponding to waveform distortion components of an analog signal to the musical sound signal data in the feedback loop may comprise a squaring circuit which squares the musical sound signal data in the feedback loop, or a level converting circuit which conducts a process corresponding to a level conversion of an analog signal on the musical sound signal data in the feedback loop in accordance with a function of a predetermined level conversion characteristic. In this case, for example, the level converting circuit may use a gain table which stores data values of the function of the level conversion characteristic, and reads out data corresponding to an input data value from the gain table, and then outputs the readout data. Alternatively, the level converting circuit may be configured so as to have programs of the function of the level conversion characteristic itself, calculate the output data from the function in accordance with the input data, and output the calculated data.
In the present invention, in a circuit in which a musical sound signal data configured by a digital signal is supplied to a feedback loop having a digital delay circuit thereby generating an echo, a delay time of the digital delay circuit is modulated with a frequency of 10 Hz or lower. According to the present invention, fluctuation components are added to an echo signal, so that wow and flutter components of a tape-recorder-type analog echo and the like can be reproduced, and a warm echo similar to the analog echo can be obtained.
Further, in the present invention, preferably, the digital signal processing circuit has a low-cut filter for removing DC components from the squared musical sound signal data.
Still further, in the present invention, preferably, the digital signal processing circuit has a cubing circuit disposed so as to generate triple components.
Furthermore, in the present invention, preferably, the digital signal processing circuit has an X-fold amplifier and a 1/X-fold amplifier connected in series, the musical sound signal is clipped by the X-fold amplifier, and the clipped signal is returned by the 1/X-fold amplifier.